A magnetic disk device as a rotational disc type storage device is used as a data storage device for a personal computer, a server or the like.
This magnetic disk device includes a disc type magnetic disk that is equipped with a recording face having a magnetic layer formed on the surface thereof and provided rotatably around a spindle shaft, a head stack assembly and a control unit for controlling reading/writing of data from/into a magnetic disk and the operation of the head stack assembly.
The head stack assembly is constructed by a head gimbal assembly, a carriage and a pivot cartridge. In the head gimbal assembly, a suspension load beam is fixed to a mount plate to be mounted on a carriage. The suspension load beam has a magnetic head for reading/writing data with the magnetic disk, and a slider for supplying an air bearing surface (ABS) to which a magnetic head is fixed. A coil support is formed at a part of the carriage, and the coil support holds a voice coil. The coil support is disposed in a magnetic field generated by a voice coil magnet and a voice coil yoke, and the voice coil magnet, the voice coil yoke and the voice coil comprise a voice coil motor (VCM) for generating driving force for rotating the carriage. The pivot cartridge is engagedly fitted in openings provided to the mount plate of the head gimbal assembly and the carriage to laminate the head gimbal assembly and the carriage. The laminated head gimbal assembly and carriage are fixedly pinched by a flange and a nut and fixed to the pivot cartridge. The head stack assembly thus constructed may be rotated around the pivot shaft.
When the magnetic disk is rotated, air flow at the surface forms an air bearing and applies buoyant force to the air bearing surface of the slider, so that the slider is slightly floated from the surface of the magnetic disk. By the driving force of the voice coil motor, the slider is turned around the center of the pivot shaft substantially in the radial direction of the magnetic disk under the state that the slider is slightly floated from the surface of the magnetic disk, whereby the magnetic head may read/write data at a predetermined position of the surface of the disk.
Such a magnetic disk device has been recently used for information electric household appliances and electrical equipment such as a notebook-size personal computer, a portable media player, a portable music player, a digital video camera or the like. In connection with advances in technology, hard disks used as data storage media of magnetic disk devices contained in information electric household appliances and electrical equipment, the magnetic disks are increased in data recording density and also microminiaturized. The promotion of the miniaturization of the magnetic disks performs developments of 2.5 type (2.5 inches (about 6.35 cm) type), and further 1 type (1 inch (about 2.54 cm) type). In the microminiaturized magnetic disk device, dimensional tolerance of the constituent devices are more remarkably small as compared with the conventional devices, and thus the processing precision and the mounting precision have been required to be more rigorously maintained. As an example, a magnetic disk and a head stack assembly are coupled to the base of a disk enclosure as different constituent devices. A slider coupled to a head gimbal assembly is designed so as to be floated from the recording surface of the magnetic disc by a fixed height under operation. Accordingly, the height of the head gimbal assembly with respect to the height of the recording surface of the magnetic disc under the assembly state must be converged within the range of the tolerance. Therefore, it is necessary that the magnetic disc is coupled to the base with high precision and also the head gimbal assembly is fixed to a pivot cartridge while rigorously keeping parallelism.
As such, a magnetic disk device has been proposed with an arcuate contact portion projecting toward a mount plate (arm) to be pinched between a flange and a nut (for example, see Japanese Patent Publication No. 8-203224 “Patent Document 1”). This contact portion is designed in an annular shape having a length in the radial direction of the flange and the nut. According to this magnetic disk device, the respective contact portions of the flange and the nut may keep the linear contact state to the mount plate (arm), and thus the parallelism of each contact face of the flange and the nut may reduce the influence on the mount plate (arm).
However, in conventional magnetic disk devices, the contact portion may be provided at only one place in cross-section in the radial direction of the flange and the nut, and thus the mount plate may be tilted along the shape of the contact portion. The reason why the mount plate is tilted along the shape of the contact portion as described above resides in that the end face of the opening of the mount plate is not supported at the contact portion. When the tilt direction of the mount plate is a separating direction from the magnetic disk, there may be considered a method of absorbing the tilt of the mount plate by adjusting the thickness of the flange or the carriage and approaching only the height position of the tip of the head gimbal assembly to a nominal value. However, according to this method, the clearance between the mount plate and the magnetic disk is reduced to a smaller value as it is nearer to the lamination portion of the mount plate with the flange and the carriage, and thus they interfere with each other with a high probability. Accordingly, it is very difficult to reduce the displacement of the height position by this method.
Furthermore, in order to prevent a situation that the pivot cartridge (hub) cannot be inserted into the opening due to production tolerance, a gap is provided between the pivot cartridge and the opening, and thus there is a case that the position of the mount plate supported at the contact portion is displaced within the range of the gap. When the position of the mount plate is displaced as described above, the height position of the head gimbal assembly is displaced.